Why finish my degree when my senior seminar project organizers are setting me up for failure?

I'm currently in my senior year of college, but considering staying for another year to fix my GPA in classes that I took when my lungs were collapsing/I was experiencing the beginnings of adult onset epilepsy (lots of seizures).

Graduation at my school requires physics majors to take part in a professor's research project, and complete a subset of it while doing various sub-tasks for the class, such as presentations, reports, and grant proposals. I am doing great on the research itself, but the requirements for the sub-tasks have been consistently vague while grades have been harsh on the non-communicated requirements. The guy leading the seminar part (not the professor doing the research) doesn't necessarily have a grudge against me, but it does seem like he is more focused on grading harshly than imparting useful knowledge. I'm trying really hard, and my professor is giving me good feedback, so I don't feel like I'm screwing up, but my grade is dictated by the one leading the seminar part, and thus isn't doing very well. I have no idea what to do to improve it, and recently I missed a meeting that was announced last-minute, because I couldn't get work off that fast, and so that's 10% of my final grade gone.

This has all led to me being extremely depressed and given me a feeling of complete helplessness. I'm going to start documenting individual cases of him doing bad stuff, and maybe report it at the end of the year, but I don't have much hope that it will do anything. It's crushing my interest in physics research and making me want to just leave. There are other career paths for me but...I'm so freaking close to graduation. I don't want to miss that sheet of paper just because of this guy's nonsense.

Have any of you guys been in this situation before? How did you push past it/did you?